Link Scheduling in Wireless Networks with Successive Interference Cancellation Shaohe Lv 1 , Weihua Zhuang 2 , Xiaodong Wang 1 , and Xingming Zhou 1 1 National Laboratory of Parallel and Distributed Processing National University of Defense Technology, ChangSha, Hunan, 410073, P. R. China 2 Department of Electrical and Computer Engineering University of Waterloo, Waterloo, Ontario, Canada 1 {shaohelv, xdwang, xmzhou}@nudt.edu.cn, 2 wzhuang@bbcr.uwaterloo.ca Abstract Successive interference cancellation (SIC) is an effective way of multipacket reception (MPR) to combat interference at the physical layer. To understand the potential MPR advantages, we study link scheduling in an ad hoc network with SIC at the physical layer. The fact that the links detected sequentially by SIC are correlated at the receiver poses key technical challenges. A link can be interfered indirectly when the detecting and removing of the correlated signals fail. We characterize the link dependence and propose a simultaneity graph (SG) to capture the effect of SIC. Then interference number is defined to measure the interference of a link. We show that scheduling over SG is NP-hard and the maximum interference number bounds the performance of a maximal greedy scheme. An independent set based greedy scheme is explored to efficiently construct a maximal feasible schedule. Moreover, with careful selection of link ordering, we present a scheduling scheme that improves the bound. The performance is evaluated by both simulations and measurements in a testbed. The throughput gain is on average 40% and up to 120% over IEEE 802.11. The complexity of SG is comparable with that of conflict graph, especially when the network size is not large. Key words: Link scheduling; successive interference cancellation PACS: 1. Introduction Modern wireless communication is interference-limited. Due to the broadcast nature, what arrives at the receiver is a com- posite signal consisting of all near-by transmissions. However, the receiver tries to decode only one transmission by regarding all the others as interference and noise. When the arrivals of multiple transmissions overlap, collision occurs and the recep- tion fails. There are two major ways to combat the interference. The first is interference avoidance, which is at the high layers to ar- range the transmission to avoid the harmful interference. This way is easy to adopt but inherently unable to provide high throughput. Many recent works show that, even with perfect network coordination, the performance is still poor [10]. The second way is to embrace the interference, i.e., all packets in a composite signal are decoded. Such capability of multiple ⋆ This work will be presented in part at the IEEE INFOCOM 2011 [16]. The authors would like to acknowledge the support of the National Foundation of Science of China (grant 61070203). packet reception (MPR) is a significant progress in signal pro- cessing. Recently, theoretic analysis [6] has verified the effec- tiveness of MPR. Following the second approach, we further ask: with the MPR techniques, do the non-MPR upper-layer protocols work well, or how to coordinate the transmissions? Though significant progress has been made in MPR tech- niques, little attention has been paid to the design of support protocols. As not all composite signals are decodable, it is in- dispensable to avoid harmful collisions (i.e., when the involved signals cannot be separated). In particular, there are specific re- quirements to ensure the feasibility of an MPR method. It is necessary to coordinate the transmissions carefully to meet the requirements. We focus on link scheduling in an ad hoc network with successive interference cancellation (SIC) at the physical layer. SIC is a simple but powerful technique to perform MPR. With SIC, the receiver tries to detect multiple received signals using an iterative approach. In each iteration, the strongest signal is decoded, by treating the remaining signals as interference. If a required SINR (signal to interference and noise ratio) is Preprint submitted to Elsevier 10 January 2011